PROJECT SUMMARY ABSTRACT The overall goal of our research is to develop novel therapeutic and detection/monitoring strategies to prevent progression of chronic kidney disease (CKD) and fibrosis. Acute kidney injury (AKI) due to ischemia reperfusion injury (IRI) or unilateral ureteral obstruction (UUO) in mice induces sustained EGFR activation and kidney fibrosis which is prevented by EGFR chemical inhibition or its genetic deletion in proximal tubule cells (PTCs). The specific EGFR ligand(s) involved remain unknown. We showed that A-disintegrin-and-metalloprotease-17 (ADAM17) proximal tubule knockout protects against injury-induced fibrosis, identifying the source of pro-fibrotic EGFR ligands to PTCs. In the injured mouse kidney, the EGFR ligand pro-Amphiregulin (pro-AREG) was very strongly upregulated and in humans sAREG was very significantly elevated in the urine of AKI and CKD patients, as well as fibrotic CKD kidney biopsies. In vitro, in human proximal tubule cells (HPTCs), sAREG induced sustained EGFR activation and pro-fibrotic targets. (Kefalogianni JCI Insight 2016). The objective of this application is to determine the role of sAREG in early vs. late injury-repair stages after AKI and to firmly link sAREG in human patient samples to kidney fibrosis and to CKD progression. Our central hypothesis is that Amphiregulin (sAREG) is the key epidermal growth factor receptor (EGFR) ligand that is responsible for inducing and amplifying pro-fibrotic EGFR signals in kidney injury. We base this on preliminary data including: (1) sAREG is sufficient and necessary to induce fibrosis after kidney injury in mice, based on sAREG injection and PTC-KO studies in mice (2) sAREG is significantly elevated in serum samples of a nephrectomy cohort of patients with CKD and its levels correlate negatively with kidney function parameters. The rationale for this project is that completion will identify sAREG as a novel therapeutic target and biomarker in CKD/fibrosis, and identify molecular mechanisms involved. We plan to test our central hypothesis with two specific aims: AIM1: Determine whether AREG is necessary for early renal recovery and/or the development of kidney fibrosis after IRI injury. AIM2: To link sAREG to degree of kidney fibrosis and stage of CKD in humans in the Boston Kidney Biopsy Cohort (BKBC, n=770) and to CKD progression in the Chronic-Renal-Insufficiency-Cohort (CRIC, n=3889). Here we will correlate sAREG serum/urine levels to kidney fibrosis on biopsy and CKD progression, and compare this to correlation with currently used kidney biomarkers (Creatinine, proteinuria). As outcomes, we expect that AREG proximal tubule knockout protects against injury-induced fibrosis and that sAREG levels correlate with CKD outcomes and perform better than current biomarkers (creatinine, proteinuria). This contribution is significant because it is expected to have impact on CKD/fibrosis detection, prevention and treatment. Our research is innovative, in our opinion, because, it would for the first time identify a kidney fibrosis biomarker that is directly mechanistically connected to the fibrotic process and could be used for therapeutic targeting and monitoring.